Methods of laser pulse development and maintenance in a compact laser resonator

ABSTRACT

Described herein are methods for developing and maintaining pulses that are produced from compact resonant cavities using one or more Q-switches and maintaining the output parameters of these pulses created during repetitive pulsed operation. The deterministic control of the evolution of a Q-switched laser pulse is complicated due to dynamic laser cavity feedback effects and unpredictable environmental inputs. Laser pulse shape control in a compact laser cavity (e.g., length/speed of light &lt;˜1 ns) is especially difficult because closed loop control becomes impossible due to causality. Because various issues cause laser output of these compact resonator cavities to drift over time, described herein are further methods for automatically maintaining those output parameters.

PRIORITY APPLICATIONS

This Patent Application is a Continuation under 35 U.S.C. 120 claimingthe benefit of U.S. patent application Ser. No. 16/198,758, filed Nov.21, 2018 and entitled “METHODS OF LASER PULSE DEVELOPMENT ANDMAINTENANCE IN A COMPACT LASER RESONATOR,” which claims the provisionalpriority of U.S. Provisional Patent Application No. 62/660,244, filedApr. 19, 2018 and entitled “METHODS OF LASER PULSE DEVELOPMENT ANDMAINTENANCE IN A COMPACT LASER RESONATOR,” and U.S. Provisional PatentApplication No. 62/589,510, filed Nov. 21, 2017 and entitled “METHODS OFLASER PULSE DEVELOPMENT AND MAINTENANCE IN A COMPACT LASER RESONATOR,”the contents of each of these priority Applications are incorporatedherein by reference.

FIELD OF THE TECHNOLOGY

Embodiments of this disclosure relate to operating a compact laserresonator in pulsed operation.

SUMMARY OF THE DESCRIPTION

Described herein are methods for developing and maintaining pulses thatare produced from compact resonant cavities using one or more Q-switchesand maintaining the output parameters of these pulses created duringrepetitive pulsed operation. The deterministic control of the evolutionof a Q-switched laser pulse is complicated due to dynamic laser cavityfeedback effects and unpredictable environmental inputs. Laser pulseshape control in a compact laser cavity (e.g., length/speed of light <˜1ns) is especially difficult because closed loop control becomesimpossible due to causality. Because various issues cause laser outputof these compact resonator cavities to drift over time, described hereinare further methods for automatically maintaining those outputparameters.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary input pulse stream waveform for controlling aQ-switch loss condition in a Q-switched laser for producing a pulsedlaser output with a stretched length or a pulsed doublet.

FIG. 2 shows exemplary real-world differences in the input pulse streamwaveform as it can be developed by electronics described further hereingiven the extreme time and voltage requirements of the waveform.

FIG. 3 shows an exemplary embodiment of instructions for processescontrolling the operational parameters of pulsed lasers describedherein, including changes to be made for various non-optimal performance“condition” for the pulsed laser output.

FIGS. 4 and 5 illustrate the diagrammatic construction of linear andring resonators, respectively, with output parameters adapted to targetmarking may be adapted using the methods herein to operate as targetdesignators based on the improvements to the output pulses.

FIG. 6 shows an embodiment using only a single Q-Switch (Pockels Cell)with two signals/conductors each separately carrying a single pulsetimed against each other (e.g., separated by Delta T) to combine into acomplex driving waveform of the Q-switch loss condition at the crystal.

FIG. 7 shows the Reflectivity R of the Q-Switch is combined and based onthe high speeds required, the reflections of the signals may be managedat the crystal, including impedance matching or termination calculationsfor the signals.

FIG. 8 shows the physical boxes for electrical driver circuitry fordriving either side of a Q-switch.

FIG. 9 shows an exemplary embodiment for a feedback system that allowscontrol of pulse in between pulse repetitions and uses a pump energycontroller as the only controlled quantity for subsequent pulses.

FIG. 10 shows shape identifiers to be used in determinations of whethera laser has a defect in the amount of gain.

FIG. 11 shows additional overlaps and creations of the Q-switched drivesignals in real-world and combinations at the Q-switch, such asdescribed in FIG. 6, along with resulting pulsed laser output waveforms.

FIG. 12 shows ideal models for pulse generation with a calculatedQ-switch Voltage wave form (QSV) showing an idealized slew rate thatovershoots the threshold significantly.

FIGS. 13 and 14 each show particular real-world examples for creatingthese input pulse streams and the electrical complexities for doing so.

FIG. 15 shows the relationship between internal intracavity fluence(E_IC) is different than exterior output (E_OC),

FIG. 16 shows details of a time-window including a rising edge of thepulsed laser output.

DETAILED DESCRIPTION

The following patent description and drawings are illustrative and arenot to be construed as limiting. Numerous specific details are describedto provide a thorough understanding. However, in certain instances,well-known or conventional details are not described in order to avoidobscuring the description. References to one or an embodiment in thepresent disclosure are not necessarily references to the sameembodiment; and, such references mean at least one. Reference in thisspecification to “one embodiment” or “an embodiment” or the like meansthat a particular feature, structure, or characteristic described inconnection with the embodiment is included in at least one embodiment ofthe disclosure. The appearances of the phrase “in one embodiment” or thelike in various places in the specification are not necessarily allreferring to the same embodiment, nor are separate or alternativeembodiments mutually exclusive of other embodiments. Moreover, variousfeatures are described that may be exhibited by some embodiments and notby others.

The systems and methods described herein may be used to maintain apulsed output with a significant repetition rate over a period of timein which fundamental operating parameters of the laser may have changed.The methods described herein include methods that seek and settle uponoperating parameters that produce pulses with desired outputcharacteristics despite changes in the operation of the laser, such asthrough the changing of temperatures or the aging of components therein.

Described herein are the innovative fruits of significant efforts atreducing such a system to practice. These efforts created methods forcreating and maintaining a pulsed output in an extremely compact laserresonator. Methods described include characterizing relationshipsbetween the laser resonator's input pulse streams and pulsed outputs,and further include options for storing in memory some of thecharacterizing data for use during the methods described herein.

One implementation may involve using these electrical signals to controlthe retardance of a Pockels cell to modulate the laser cavityreflectivity. For example, input pulse streams may be adjusted to createthe desired pulsed laser output initially, after a reset, or to createstarting points for the Q-switch loss condition, as described furtherherein. As another example, a set or fixed input pulse stream (e.g., oneof a number of chosen input pulse streams) may be used to create anoutput pulse, while the output pulse may be tuned with an adjustment ofthe gain provided by a gain module, such as to modify the input to apumping source of the gain module, such as a pump diode that opticallypumps the gain module.

Methods described further include methods of resetting pulsed output.The resetting processes described herein may be used manually by anoperator to reset the pulsed laser output and/or automatically by thelaser system if the pulsed output falls outside of specifications forthe pulsed output (e.g., outside of output specifications for over athreshold number or percentage of repetitions). For example, describedfurther herein is a method of quickly settling on a new input pulsestream based on creating an intentionally-degraded pulse output,analyzing it, and determining, based on calculations from the degradedoutput, a new input set of pulses designed to create the desired output.While some of the operation of the Q-switches described herein relies onprior knowledge of Q-switched lasers, the specific method steps detailedand claimed herein are surprising in their application to creatingconsistent pulsed outputs from an ultra-compact resonator, stretching topulse lengths encompassing many roundtrip times of the resonator, andrepeating the process over many epochs spanning several differentoperating conditions.

The evolution of a giant laser pulse through Q-switching dependsstrongly on the initial conditions of the resonant laser cavity. Basedon these conditions, the most important being the ratio of gain to lossof the optical cavity, the temporal shape of the output laser pulseevolves over time via the timing and amplitude of the input pulse streamcomprising the Q-switch loss condition and based on the gain within thelaser due to the pump energy applied to the gain medium. This gain/lossratio controls the time-formation of the optical pulse which isessentially the time-evolution of a differential equation. Therefore,the gain/loss ratio is intrinsically tied to the Q-switch loss conditionin developing and maintaining a pulsed laser output over multiplerepetitions. The disclosure herein describes many methods of developingand maintaining pulsed laser outputs within laser specifications overlong periods of time and with the ability to re-establish pulsed laseroutputs within specification with user intervention and/orautomatically.

In solid state lasers, the laser crystal provides optical gain throughstimulated emission of stored energy. Light exits the laser cavitythrough two effects: outcoupling and loss. In this description“outcoupling” describes light that leaves the laser cavity (e.g., asenergy in an output pulse), and “loss” describes light that is lost inany other way.

In order to achieve efficient conversion of stored energy to outputlaser pulse energy, the gain is typically much higher than the sum ofthe loss and the outcoupling. The ratio usually varies over a factor oftwo or more. If this ratio is too low, the loss term dominates the laseraction, causing undesirable inefficient laser performance. A very highgain-to-loss ratio implements efficient lasing action, and creates anoptical pulse with a temporal length on the order of a few opticalcavity round trip times. In one embodiment described further herein, anexemplary system implements a gain of approximately 4, a loss ofapproximately 10%, and an outcoupling of approximately 50%. Thisdescribes a laser configuration that is nearly “optimally” outcoupled[Siegman, Degnan 1989]. Indeed, the methods herein may be used withvarious configurations of operating parameters for resonators aseffective methods for repeatedly and efficiently settling on new inputpulse streams as those operating parameters change.

As described in the literature, the optimally outcoupled laser pulse isthe one that outcouples the maximum pulse energy for a given set oflaser parameters. It is important to note that the equations in thesereferences denote a static laser cavity reflectivity parameter. Thedescription herein discloses laser operation with a variable lasercavity reflectivity which changes significantly over the evolution ofthe optical pulse while outcoupling a laser pulse with energyapproximately equal to the “optimally” outcoupled laser previouslydescribed.

In a compact laser resonator (e.g. cavity lengths less than 30 cm), theoptical round-trip time may be smaller than 1 ns. This time scale isimportant because it represents a causality limit on closed-loop pulseshaping control systems. In a compact, efficient laser resonator asdescribed, the combination of short round-trip time and high gainresults in a laser pulse that is on the order of 1-10 ns long. It isdifficult to reliably detect this laser pulse formation, determine acorrective action, and implement the corrective action in such a short,efficient laser cavity because the laser pulse may evolve in anundesired way past the point of control before a light speed signal canreach and return from a nearby control system. These configurations ofcompact and efficient laser resonators function to limit the options forclosed-loop control of optical pulse formation.

The specification requirements for output pulses are significant—anexemplary standard has high power and short stable pulse width withparticular requirements for top hat squareness. This is a significantrequirement alone, but it is made more stringent when attempted by acompact resonator. An exemplary compact resonator described herein is asmall twisted ring cavity with a round trip time of about 1.5 ns, orabout 10% of the desired pulse width output of 15 ns. Prior techniquesfor stretching a stable pulse while limiting lasing during the pulseuntil a desired width is achieved are ineffective when feedback cannotbe sensed and responded to quickly enough to affect the present pulse.Particularly, during the efforts of reducing these pulse generation andmaintenance methods to practice, even while using a human operator andhand-controlled feedback, the process of automating these methodspresented significant challenges to devise methods that consistentlycreated an output pulse that fit specifications. These differenttechniques have been developed, reduced to practice, and describedherein for operating lasers such that they reliably and repeatedlyoperate with output pulses within specification, despite the interplaybetween many operating characteristics of the laser in the sensedcompleted output pulse that serves as the feedback information forcreating the next input pulse.

Therefore, in sharp contrast to prior methods, the processes describedherein provide required critical control of the input pulse streamoutside of the pulse time frame because the input pulse stream must beso compact, no present feedback could be generated in time to affect thepresent pulse. Therefore, we describe further herein how to control theoutput pulse generation solely based on reviewing and analyzing theprior outputs of the resonator. Therefore, special techniques weredeveloped to analyze the convoluted output and determine input pulsestreams and other operating parameters for creating, maintaining, andmodifying pulsed outputs over many epochs and over long periods of time.While the operating parameter of the input pulse stream is a large focusof this description, there are other parameters that are similarlycontrolled and recorded such as pump power and various temperatures ofthe system (e.g., gain medium temperature, pumping source temperature).

Q-switched lasers are a class of lasers in which energy is stored withina gain material during pumping while a cavity is “spoiled” or has a verylow Q-factor. The stored energy is then released as an energetic opticalpulse by rapidly switching the cavity to have a high Q-factor. Twocommon implementation examples of Q-switched cavities for linear andring resonators are shown in FIGS. 4 and 5, respectively.

In these two examples, a Q-switch (QS) is implemented as one or morePockels cells which receive a voltage signal that results inpolarization rotation of the intracavity optical radiation. Whilepumping the gain medium prior emitting an optical pulse, an intra-cavitypolarization output-coupler spoils the cavity so that a significantportion of spontaneous emissions from the gain medium is notrecirculated in the cavity and lasing does not occur. The intra-cavitypolarization output-coupler may simply be any optical element which hasa different transmission or reflection in two orthogonal polarizations.To emit an optical pulse, the voltage waveform to the Pockels cellinduces a polarization rotation (including zero rotation) for which thepolarization output coupler results in a very high proportion ofre-circulated radiation within the laser cavity. Under these conditions,the radiation experiences a round-trip cavity loss that is less than thegain experienced by the gain element and lasing occurs. When lasingoccurs, an optical pulse is emitted, and the optical gain is rapidlydepleted until it falls below the cavity loss. Once the gain falls belowthe cavity loss, lasing is suspended and the pulse ends. The process forgenerating an optical pulse is dynamic, since the emission intensity atany time depends on the cavity loss and gain of the crystal.Additionally, the dynamics depends on a response time for the cavitywhich is related to the round-trip time within the cavity. Generally, itis difficult to create optical pulses that are much longer than thetimes required for a few optical round trips of the cavity. This isbecause the energy with the crystal is rapidly depleted as soon as thegain/loss ratio of the cavity exceeds unity. Consequently, constructionof small Q-switched lasers with small cavities that are capable oflonger pulse lengths is a significant advance over the state of the art.

The present disclosure utilizes a parameterized Q-controlled cavity toprovide a longer pulse length. Instead of switching the laser cavitybetween a spoiled state and a high Q-state, the disclosure hereinincludes one or more intermediate Q-states that are pre-programmedbefore pulse generation begins in level and timing to produce a longersingle pulse after iterative refinement from conditions producingmultiple pulse peaks. The previous two illustrated Q-switch cavity typesare merely examples and many other configurations are well known bythose skilled in the art. However, these configurations have theattribute that the effective reflectivity and transmission at the outputcoupler is controllable permitting efficient energy extraction atintermediate Q-factor settings for the cavity. The pulse-extendingmethods described herein were implemented and reduced to practice usinga twisted ring cavity, such as those previously disclosed in U.S. Pat.No. 9,225,143.

Described herein are systems and methods for producing and maintainingrepetitive pulsed outputs from laser with repetition rate. These pulsedoutputs, including stretched pulses and multiple pulses, which includesseveral varied processes for settling a pulsed laser output for aparticular goal (e.g., by analyzing a portion of the pulsed laser outputfor a quality or for an attribute) and then by adjusting the inputs tothe laser for the next repetition or a subsequent repetition of thelaser, including one or more of a part of the Q-switch loss condition ora pump energy provided to gain media. Various methods are describedherein that provide novel advantageous ways to develop and maintain overrepetitions these pulsed outputs meeting various criteria. Although insome embodiments a flat-topped pulse is shown with an ideal ornear-ideal “top hat” shape, other pulse shapes and types will fitvarious other specifications. Therefore, while other shapes aredescribed under one specification as ideal, it may be described byanother specification as not ideal, degraded, or entirely failing. Forexample, a doubled pulse may be a desired output for one specificationand that pulse shape may fail another specification and otherwise be adegraded pulse option that can be used for diagnostic purposes, asdescribed further herein. Therefore, when described herein as degradedor degenerated pulses, the terms are used relative to a particularspecification, and the disclosure herein for creating that pulsed outputoption can be used for any of the types of processes described herein.

Described herein are processes and systems for achieving this repetitivepulsed laser output in harsh and changing conditions. When conditionschange, these described methods and systems are able automatically tosense repeated pulsed laser outputs that are shifting away from ideal orfrom acceptable for the standard and to find a way back automaticallyvia stored processes and control systems, including within the laser.These processes include processes that have secondary quick settlemethods, such as creating degraded pulses as described further herein.Under changing conditions, the operational points of various portions ofthe laser change and the interaction with the Q-switch loss conditioncan change significantly. Therefore, methods and systems are describedherein to produce and maintain repetitive pulsed laser outputs overharsh and changing conditions.

In systems and methods herein, repetitive pulsed laser outputs arecreated by lasers such as those shown in FIGS. 4 and 5 using a rampdelivered to a Q-switch (e.g., a Q-switch loss condition) like thoseshown in FIGS. 1 and 2. These repetitive pulsed laser outputs includeexemplary repetition rates of 10 per second, 20 per second, 100 persecond, or 1000 per second, for example, representing periods ofrepetition from 100 ms, 50 ms, 10 ms, and 1 ms respectively.

FIGS. 1 and 2 show the differences between ideal and real-world inputpulse streams, including non-ideal features such as rounding and slewrates. These exemplary embodiments of an input pulse stream are used forcreating a stretched pulse or for creating a pulsed doublet as describedherein. In one embodiment, the cavity Q-factor is dynamically generatedby a single high voltage waveform generator and provided to a singlePockels cell. However, in other embodiments the voltage waveform may becomprised of two separate voltage pulses that are additively combined atthe Q-switch for an effective two-level Q-switch, such as shown in FIG.6. For example, pulsed voltages of opposite polarity may be applied toopposite leads of a Pockels cell. Alternatively, voltage pulses may beadded in series to produce an effective two-level voltage differenceacross a Pockels cell. In another embodiment, as shown in FIGS. 4 and 5,two separate Pockels cells may be used, with each Pockels cell receivinga separate voltage pulse so that the total radiation polarizationrotation within the cavity corresponds to a single effective inputvoltage waveform having two levels.

In the currently described class of embodiments, the input voltagewaveform (whether an effective waveform or actual waveform) can bedescribed with the primary parameters: HV1, HV2, ΔT, and ∂V/∂t of bothramps. HV1 and HV2 are the first and second voltage levels, and ΔT isthe time delay between the first and second voltage pulses, that may bemeasured between different portions of the combined input pulse streamwaveform for the purposes of consistent control of the Q-switch losscondition between repetitions of pulses.

As shown and described herein, ΔT or “Delta T” may be measured betweenseveral points on the Q-switch loss condition waveform. This time delaymay be measured as a difference in time when capacitors are opened to acombined signal, such as shown in FIG. 13, as a difference in time whenthe combined signal reacts to the connection of the multiple highvoltage capacitors creating the signal, the difference in times betweenwhen the combined signal reaches a certain levels, etc. These levels maybe consistent for the beginning time and ending time, or may be chosenconveniently, such as noting the difference in time when signals weresent to the laser. The important feature is the ability to control thistime between repetitions of the laser to affect control of theintracavity fluence to effectively merge and stretch the pulses as shownin FIG. 15. Therefore, the descriptions and multiple drawings ofmeasuring Delta T may be understood as multiple different disclosures ofconsistent measurement schemes designed for the control of the pulsegeneration methods in the lasers herein.

During the transition between the first voltage ramp ∂V/∂t to the firstvoltage and the second voltage ramp ∂V/∂t to a second voltage pulse, thetwo voltage ramp rates ∂V/∂t provides further description of the voltagewaveform, such as shown in FIG. 11. These voltage ramp rates are relatedto the real-world slew rates in FIG. 11 established from connecting acapacitor holding the high voltage with a side of the Q-switch, such asshown in FIG. 13. Though many described embodiments use two voltagelevels for the Q-switch loss condition, the approach may be extended tosingle or other multiple voltage levels in additional embodiments.

In one class of embodiments, the parameters ∂V/∂t for the ramps relatedto HV1 and HV2 may be fixed by the hardware architecture or voltagegenerator parameters and specified output optical pulses may be achievedthrough iterative refinement of the HV1, HV2, and A T waveformparameters. Because the end point of the first ramp to HV1 determinesthe plateau value shown in various input streams shown and describedherein, the HV1 values matter both to the real-world creation of the∂V/∂t for the first ramp from a nominally zero voltage as well as theheld/returned to value during the ΔT time period. The HV2 voltage sets asecond voltage ramp, again potentially like the high voltage capacitorswitched into connection as shown and described further herein, butafter attaining a certain voltage on the Q-switch, additional HV2voltage will not extract more energy into the later part of thestretched pulse or the second pulse of a pulse doublet. Therefore, themodifications of HV2 may be limited in their ability to alter the shapeof pulsed laser output by comparison to the changes in HV1 and ΔT in theQ-switch loss condition. In addition, as described further herein,non-optimal values for HV1 and ΔT result in specific symptoms in theoutput optical pulse that can be diagnosed for subsequent iterativecorrections to HV1 and ΔT. Additionally, as described herein, energy ofthe pumping may be used to modify a pulsed laser output.

In many embodiments, including when the laser is being first operated,the laser pulse must be built from a small set of assumptions. Whenfirst building an input pulse stream like the ones shown in FIGS. 1 and2, there may be only estimates of a pump energy for pumping the gainmedium. Stored values may exist for an HV1, such as 1800 V or anothervalue based on an estimate or calculation of the reflectivity of theQ-switch, described further herein. This value may also be calculated tobe affected by a pumping energy and gain efficiency, also describedfurther herein. Stored values may be used for a building the process, asdescribed herein, to shortcut the process of developing and maintaininga pulsed laser output over multiple repetitions. Initially building thispulse may be performed in controlled environments, such as in a lab, orin operational environments such as in the field, or with uncontrollableconditions. Each of these pulse development environments also needs tobe able to maintain the pulsing operation as well, so the processes ofdeveloping and maintaining are sometimes discussed interchangeablyherein. For example, as a process of maintaining a pulsed laser output,processes herein may deconstruct or degrade a pulsed output by changesto the Q-switched loss condition or pump energy and then after analyzingthe pulsed laser output, may build the pulsed laser output toward aspecification based on the analysis.

In one embodiment, an initial phase of building a stretched pulse or apulse doublet includes starting with a series of pulses starting with aninitial stored or calculated value of pump energy and related Q-switchloss conditions including increasing HV1 voltages that areestimated/calculated/stored/known to be near a threshold of lasing forthe laser. Each building of a pulse in the laser described herein may bestarted from few initial conditions by choosing a pumping energy andstarting to pulse the HV1 without a subsequent HV2 ramp (e.g., a singleinput pulse) and using an increasing voltage for HV1 until the laseroutput begins to pulse in response. HV1 can be increased until a strongfirst pulse is achieved, pulsing the laser to a portion of its potentialwith a HV1 above threshold while either leaving the HV2 ramp absent,leaving Delta T far too long to have a pulse overlap, and/or leaving HV2at or near zero. Each of these elements provides a lack of a second halfof the input pulse stream and lack of full extraction from the laser.Thus, the energy of the initially generated pulse will be some fractionof the final expected energy based on the pumping level first used.

Sometimes with a sufficiently large HV1 voltage value and interaction ofthe voltage ramp with the gain stored by the pump energy, the initialpulse may create a secondary pulse. However, this secondary pulse is nota controlled or controllable artifact if produced inadvertently.However, a second pulse may be generated intentionally as describedfurther herein, including using an HV1 value sufficient to cause lasingand a long Delta T before a second ramp to a greater voltage. Further asshown and described in FIG. 12, there are ideal ramp rates and timingsfor each of these slopes, given a host of incalculable parameterschanging constantly. Therefore, the described methods are useful forproducing and maintaining pulses given real-world operating parametersand changing operating conditions.

In some embodiments, HV1 and its associated ramp rate may be controlledto achieve the lasing threshold of the laser at a repeatable time, thuscontrolling the jitter of the rising edge between multiple repetitionsof the pulsed laser output. For example, in some embodiments, shiftingHV1 or its ramp rate or slew rate will shift when the input pulse streaminduces the rising edge of the pulsed laser output. In otherembodiments, HV1 reaches a peak and then undergoes a depression beforethe HV2 ramp is added into the signal of the Q-switch loss condition. Asshown further herein, there may be overshoot of the HV1 signal as partof controlling the ramp or slew rate in the initial rise toward HV1.

As described further herein, repetition of pulse instructions orinstructions to make a pulse, such as a Q-switch loss condition and apump energy will assume a repetition of the pulsed laser output (e.g.,with some repetition rate) and will refer to the repetitive instructionssent to the laser for producing the repetitive pulsed laser outputs. Therepetitive instructions may be controlled by computer control, includingby some level of human control. For example, repetition rates andcertainly Q-switch loss conditions may be faster than can be controlledby humans, but longer-time-scale parameters may be controlled by humanoperators. The processes required to set the correct controls for theoperating parameters, including input pulse creation, the pumping power,and other lasing controls may be controlled by computer both with andwithout human intervention, including via control panel (e.g., radiobuttons, entry of values), and/or operated automatically by processesrun by computer described further herein, and/or controlled by otheroperational controllers for performing the described methods ofcontrolling the pulsed operation of the laser.

In one embodiment of a method of initially developing/settling astretched pulse or pulse doublet, after an initial single pulse isgenerated with an HV1 voltage and its associated voltage ramp, themethod includes creating an additional pulse in a pulse doublet in asubsequent repetition by introducing an HV2 ramp after a very long DeltaT into the input pulse streams. These very long Delta T values may besufficient to create an entirely separate pulse in a pulse doublet onthe next repetition and may include a time that is on the order of theinitial pulse length or multiples thereof. This second ramp will createa second pulse by continuing to increase the reflectivity of a singleQ-switch or the combination of multiple Q-switches in the cavity.

Thereafter, the two pulses in the pulse doublet may be balanced asdescribed further herein with respect to FIG. 3 for adjusting HV1, DeltaT and pump energy for subsequent pulses. For example, if the secondpulse of the pulse doublet has more energy or a greater power maximum,HV1 may be increased on a subsequent repetition of the pulse.Alternatively, as described with respect to FIG. 3, pump energy could beincreased on a subsequent repetition of the pulse. With two pulsesbalanced, a pulse doublet may be maintained by monitoring the balancedpulses and continuing to adjust the inputs to the laser as needed anddescribed with respect to FIG. 3.

For embodiments where a single stretched pulse is desired, additionalportions of FIG. 3 may be used and Delta T may be decreased while thebalance of power and/or amplitude is maintained during subsequentpulses. Additionally, degraded pulses may be stored for use insubsequent recovery of pulsing operation, as described herein for usewhile trying to regain stretched pulse operation (e.g., withspecification) and an intentionally degraded pulsed laser output is usedto analyze the pulsed laser's operational conditions and to develop anew input stream and/or pump energy to adapt later pulsed laser outputs.

FIG. 3 shows an exemplary embodiment of instructions for processescontrolling the operational parameters of pulsed lasers describedherein, including changes to be made for various non-optimal performance“condition” for the pulsed laser output. These changes include onlychanges to HV1, Delta T and Pump Energy and produce initialconsiderations for changing those values based on the methods describedherein for developing and maintaining the pulsed output on subsequentrepetitions. For each of these conditions, there may be multiple relatedactions, each of which may be taken or optimized by the processes and/oreach may be excluded or minimized by the processes. In other words, onlyone or several of the actions may be performed by a method describedherein in response to a particular condition, including based ondifferent analyzed information indicating favoring one action overanother, such as an action that would imbalance another feature of thepulsed laser output. Additionally, in embodiments of methods and systemsdescribed herein, a single controlling action, such as changing the pumpenergy, may be used for all controls between one pulse and adjusting fora subsequent pulse.

In FIG. 3, the term “saturation” simply means that the optical signaldetected as the pulsed laser output exceeds a threshold, such as aphysical saturation level of a detector, or a threshold that is appliedin the electronics system, or a threshold in software. As noted herein,this indicates a high power during that period. As shown in the figure,the early saturation and late saturation relates to timing of thesaturation, if it occurs, relative to the timing of delta T and rise inHV2. A late saturation event occurs when HV2 is needed to createsufficient emission and the energy of the laser is concentrated (to asaturated level) in the later part of the pulsed laser output. If asaturation occurs at a later time, this could indicate that the HV1 istoo low, and it should be increased to permit greater energy extractionat earlier times, or it may indicate that the time difference should beincreased to separate emissions related to the HV1 and HV2 ramps, oralternatively that the pump energy should be increased. If the opticalsignal results in a saturation that is early in time, then the laser isreleasing all of the gain mediums energy prematurely. Therefore, eitherthe first voltage level HV1 should be decreased or the laser pump energyshould be decreased on a subsequent pulse repetition.

A pulse doublet occurs if the pulsed laser output appears to have twodistinct local maxima. Local maxima should be understood to besufficiently low-pass filtered to remove noise or bounce around theoutput power of the pulsed laser output. Thus, a zero-crossing of aderivative of a low-pass filtered signal would indicate a real shift inthe emission rate causing a maximum or a minimum. Having two maxima witha local minimum in between can be considered as having three suchzero-crossings of the first derivative of a sufficiently low-passfiltered output power of the pulsed laser output. These two peaks may beseparated by some time and by a valley of emission energy in the pulse.As described above, balancing the peaks of a doublet is important forcreating a single stretched pulsed laser output, while reducing the timeseparation between voltage ramps, Delta T. In either instance wherethere is a pulse doublet, the time separation ΔT may be reduced, howeverother options for actions may be used.

Pulsed laser outputs may show a skew in the top or maximum power portionof the pulsed laser output, those described and shown in FIG. 10 withabout 1% extra/higher gain or with about 1% less/lower gain conditionsas described further herein. As described further herein, this conditionof skew in the pulse may indicate multiple or a combination of actions,some of which are limited in scope for the purposes of methods describedherein to improve the processes of settling the pulsed output.

If the skew of the pulsed laser output is skewed toward an early side ofthe pulsed laser output (or “skewed left”), this could indicate eitherthat HV1 is too large (e.g., achieves a ramp slope too quickly for thestored gain) or that the pump energy is too large. The pulsed in suchsituations may also show an earlier output maximum for the pulse if theshape is not further analyzed. Alternatively, if the skew of the pulsedlaser output is skewed toward a late side of the pulsed laser output (or“skewed right”), this could indicate either the HV1 may be too small orthe pump energy may be too small.

In some cases, such as when the pulse is first being developed, thepulsed laser output has two peaks which are symmetric, but the peaks aretoo wide to create a stretched pulse. As described herein, this may be adesired output for a pulsed doublet. No particular changes in HV1 orpump energy can bring the two peaks as quickly together so no otheractions are indicated for this condition. As described above, thestep-wise process for first developing a stretched pulse balances twopulses that would be classified in these conditions as “balanced toowide” and thereafter, the process decreases Delta T. Alternatively, ifthe time separation ΔT becomes too short, a symmetric pulse that is tooshort will be produced and the Delta T may be increased in response.

As described further herein, time-windows may be used to measure theenergy of portions of the pulsed laser output or the entirety of thepulsed laser output, such as to determine whether the output includesthe correct extraction of the pumped energy for that pulse repetition.As shown in several drawings of exemplary pulsed outputs, degradedpulses fail to extract all the energy that a properly stretched pulsewill extract due to the increase intracavity fluence shown in FIG. 15during the stretching of the pulses. This increased period of peakingthe intracavity fluence and subsequent control based on the sensedoutput, which appears so different, are important elements to severalmethods described herein. For example, the convoluted connectionsbetween the building phases of the laser pulse and the ramp rates of theQ-switch loss condition lead to multiple different conclusions,particularly as detailed in FIG. 3. For example, in response todetermining that the output contains too little pulse energy, the HV1value may be decreased, which as described herein would actuallydecrease the pulse power at the rising edge but would increase theoverall pulse energy of the pulsed laser output. In addition, alternatemethods can combine raising or lowering the pump energy in response toan output pulse that has either too little or too much pulse energy,respectively.

Many of these conditions and actions are described further hereinrelated to methods for producing and maintaining pulses with respect toeither resetting operation of the pulsed laser output withinspecification from a period of non-operation or improper operation, oralternatively maintaining proper operation when issues are spotted.Additional information may be used from the figure for increasingsettling accuracy or speed, such as described herein with quick settlingtechniques.

Described herein are methods of controlling the pulsed lasing of a laserby modifying input pulse parameters and/or pump parameters either viauser input as shown above or via automatic control using these methods.An operational laser builds and maintains a pulsed laser output meetingspecifications consistently over many repetitions. Therefore, a maingoal of the methods described herein is quickly settling on anoperational input pulse stream that properly creates an output pulsewithin specification, and doing so consistently over a period time andmany thousands or millions of repetitions. This process of settling mayhappen quickly using methods herein, or may not be able to happen at alldue to the sensed laser output comprising a convolution of many inputparameters and conditions requiring an unknown combination of amultitude of actions to create a settled pulsed laser output withinspecification given some compact laser resonators. Even such lasers whencontrolled by human operators with human-controlled computer interfacesmay fail to be able to settle on operational input parameters thatcreate settled repetitive outputs of pulsed laser outputs that meet aspecification. Therefore, methods of operating these lasers describedherein are specifically adapted to quickly settle, settle after losingoperational parameters that produce a desired pulsed laser output (e.g.,it falls out of specification) such as due to changing operatingenvironmental parameters, and prepare stored characterization dataregarding these settling characteristics of the laser for later use.

Some embodiments of methods herein include general techniques forcontrolling the production of repeatable repetitions of the pulsed laseroutput within specification. These methods include receiving a first setof Q-switch input pulses comprising a first input pulse streamcontaining an HV1 pulse and an HV2 pulse separated by a delta timebetween the rise to a first HV1 voltage and a rise to an HV2 voltage foruse in creating a first pulsed lasing event in a laser resonator. Asdescribed herein the Delta T may be measured from beginning of a firstrise and the beginning of a second rise in the Q-switch loss condition.The method may further include receiving a first indication of an errorin the pulsed lasing event, such as a condition in the described table.Based on the indication of the condition or error, the method thencreates a second input pulse stream that is adapted for use in the laserresonator that changes one or more inputs and takes one or more of theinputs in the figure. The method then creates the subsequent pulse bytransmitting the second input pulse stream to the laser.

Multiple different embodiments for this control process are describedthat conclude the method should take steps to shift the laser'soperation that are illogical or otherwise counterintuitive, and thatserve nevertheless to correct the pulsed laser output shape. In oneembodiment, the determining step concludes that the error is poweroutput being too low for the first pulsed lasing event and thereafterthe method decreases the HV1 pulse in response for a subsequent pulse inresponse. In one embodiment, the determining step concludes that theerror is power output being too high for the first pulsed lasing eventand thereafter the method increases the HV1 pulse in response for asubsequent pulse. In one embodiment, the determining step concludes thatthe determining step concludes that the error or issue is late peakingof the first pulsed lasing event and thereafter the method increases thedelta time in response to the error being late-peaking of the firstpulsed lasing event.

In one embodiment, the method is successful in correcting the pulseafter the claimed attempt at changing the input pulse stream and, aftercorrecting the input pulse stream for the second pulsed lasing event,the method includes receiving a second indication that the second pulsedlasing event in the laser resonator does not include the error. In oneembodiment, the method has a further determining step that determinesfrom the second indication that the second pulsed lasing event has asecond error and thereafter the method modifies HV1 for a third inputpulse stream based on the second indication. The method may besuccessful and thereafter transmit a plurality of corrected input pulsestreams containing the correction. In one embodiment the method includescreating a plurality of input pulse streams that maintain the HV1voltage used in the second input pulse stream transmitting the pluralityof input pulse streams, such as to the laser system, to a Q-switchwithin the laser system, for use in creating a plurality of pulsedlasing events in the laser resonator following the second pulsed lasingevent.

In some embodiments, the methods allow for a prepared method for quicklysettling on an input pulse stream based on analysis of anintentionally-degraded pulsed laser output that was created with anintentionally-created test input pulse stream that is adapted to createthe degraded pulsed output. This degraded pulsed output is used by theprocesses herein in order to discern the correct input pulse stream toapply to the Q-switches in order to quickly return operation to arepeating pulsed output within specification.

Discerning the causes of various issues (spurious portions of the pulse,pulse outside of one or more specifications) is complicated by theconvoluted effects of various operational parameters of the laserresonator can be managed, nevertheless, the described methods includereliably settling on new operational parameters that produce pulseoutputs that are within specification within a minimum number of missedpulses or pulses not meeting specification. These methods of quicklysettling on new operational parameters include novel steps of creatingdeliberately degraded outputs, which may include two or more pulsescreated in per pulsed repetition. In an exemplary case, first a desiredoutput pulse shape is created during laser manufacture via manualadjustment of the control voltage. Then a significant delay is addedbetween the HV1 and HV2 pulses such that the delay is much larger thanthe output pulse width. This delay causes the generation of two distinctoptical pulses, each having a shape more simply described byconventional laser models. The characteristics of this prototype pulsedoublet is then saved to the memory of the control system. In autonomousoperation the control system first creates pulse doublets using the samefixed delay, and analyzes the shape (e.g., time, amplitude, and width)of each pulse to determine corrections to be made to the control signals(e.g., HV1, ΔT, HV2). Once those changes to the control stream areimplemented, the delay is removed, and the optimal optical pulse shapeis generated in subsequent iterations.

There may be several measurements used by the methods herein todetermine the effectiveness of a settling method and as shown in thefigures, there may be many actions to take in response to any conditionsensed in the pulsed laser output. Therefore, methods of maintaining apulsed laser output may vary sharply in their efficiency in finding anew input pulse that produces a settled pulsed laser output after, forwhatever perturbing reason, a prior settled operation of the pulsedlaser output was lost. The settling method will start with a pulseoutput that is recognized as needing an improved output pulse stream byfinding a newly-settled input pulse stream. This decision may begin anew process as described herein whereby a new input pulse stream issought and refined via various process steps, namely a settling process.

For example, the settling process step may include creating adegenerated pulse output and measuring a difference with a stored (e.g.,expected) output parameter related to the degenerated pulse output. Themeasurements of this process may include a number of repetitions (e.g.,cycles of the repetition rate) that are needed to regain a settledpulsed output reliably that is within specification, and repeatedly so,or the number of repetitions that are missed (e.g., the number of missedpulsed outputs had the laser operated normally) between a beginning andend point of the process.

The beginning point of the method may be a noticed or recognized pulsedoutput that is out of specification or developing features that wouldlead it to be out of specification if those features became more/lessprominent, a point where a decision is made to correct the pulse, and afirst repetition where corrective steps are taken thereafter. The endpoint of the method may include achieving a settled input pulse stream,applying that input stream to the resonator to produce an output, andthe first pulse that is output or measured that is again withinspecification. This missed number of outputs measured between thebeginning and ending points of the method is referred to further hereinas the number of corrective repetitions that are missed due to a newsettling process undertaken due to a noticed failure of the pulsedoutputs to meet specification.

The discussion of steps herein for determining the next input pulsestream is defined by a repetition period, which is the period of timebetween repetitions of pulsed outputs to meet specification (e.g.,periods from about 20-100 ms) and the steps taken during that repetitionperiod, including steps for sending an input pulse stream to theQ-switch(es) in time to generate a pulse at or near the time for thenext repetition. The terms intentionally “corrective” and intentionally“degraded/degrading” are used herein to distinguish two distinct ways ofchoosing the next input pulse stream in the process of settling on aninput pulse stream that creates again a desired output pulse stream thatmeets desired output pulse specifications. Where the next-selected inputpulse stream is targeted at getting a new output pulse that isintentionally moved toward a desired output pulse that next input pulsestream is intentionally corrective. Where the next-selected input pulsestream that is targeted at getting a new output pulse that isintentionally moved away from a desired output pulse, such as bydegrading the pulse to a pair of two pulses that may be analyzedseparately (e.g., such as by measuring a gap between the pulses or itsotherwise degraded forms).

There are quick-settling processes for sampling and analyzing pulsedlaser outputs and that include creating a degraded pulse to aid in thatanalysis. A degraded pulse creation includes a creating anintentionally-degraded pulse that could include a degraded outputcreated by the intentionally-degraded input pulse stream. For example, adegraded pulse would include a pulse doublet being created in a processthat is otherwise seeking to produce a stretched single pulse. Thepurpose of the degraded pulse creation is to probe the laser system'soperational parameters and to analyze a likely path to quickly settlingthe system, such as, in one embodiment, by changing the pump energywithout disturbing the rest of the Q-switch loss condition. As describedfurther herein, the system may have some tested parameters providingsome known way-points from which a difference in output may be measuredwith respect to a deviation in input. By utilizing these differences, asdescribed herein, the methods may be configured for quick settling on aset of operational parameters using a combination of stored operationalparameters and using deviation calculations to create quick settlingmethods.

In one embodiment, a quick settling method of operating a pulsed-outputlaser includes first operating a pulsed-output laser by sending a firstinput pulse stream to a Q-switch in the laser such that the lasercreates a first single-pulse lasing event in the laser. The methodthereafter includes selecting a second input pulse stream such that thesecond input pulse stream is adapted to create an expected double-pulselasing event in the laser. For example, this input pulse stream could becreated by changing the Q-switch loss condition by creating a very longDelta T to create a pulse doublet. The method includes second operatingthe laser with the second input pulse stream to the Q-switch such thatit creates a detected double-pulse lasing event in the laser. The methodthen analyzes a lasing difference between the detected double-pulselasing event and the expected double-pulse lasing event. For example,the expected double-pulsed lasing event may be expected to have balancedpower, whereas the received double-pulsed lasing event may include animbalance, suggesting a correction or multiple possible corrections forcreating a subsequent pulse as described above. The method includesdetermining, based on the analyzed lasing difference, a modificationfrom the first input pulse stream to improve a performance parameter ofthe first single-pulse lasing event in the laser. For example, inaddition to reducing Delta T to the time that was used previously, anenergy or a voltage level may be changed for a subsequent pulse. Themethod then operates the laser with a third input pulse stream includingthe modification to the Q-switch such that the laser creates a secondsingle-pulse lasing event in the laser with an improvement in theperformance parameter.

Multiple options may be used for this quick settling using analysis of adegraded pulse doublet. In one embodiment, the method repeatedlyoperates the pulsed-output laser in with a repetition rate of pulsedoutputs, wherein first operating, second operating, and third operatingare performed on periods of the repetition rate. Thus, the laser mayoperate continually in synchronous operation with other components orwith an expected repetition. In some embodiments, the next pulse may beimmediately following, in other words, such that the third operating ona period of the repetition rate immediately following the secondoperating. In one embodiment, the method is performed completely onsuccessive repetition periods, such that wherein first operating, secondoperating, and third operating are performed on successive periods ofthe repetition rate.

The method may further include analyzing a first single-pulse lasingevent in the laser and for preparing the second degrade pulse doubletevent, calculating a first parameter of the expected double-pulse lasingevent from an analyzed measurement of the first single-pulse lasingevent. This embodiment allows the methods to include multiple differentdegraded pulsing events, such as to measure different changes needed tobe revised for the next non-degraded pulse event sent to the laser, forexample, in selecting parameters for the second input pulse stream. Forexample, the method may use analysis of the first single-pulsed lasingevent, such as an error that was smaller or more minor versions of theissues identified herein for conditions of pulsed laser outputs andactions for correcting same. In other words, the methods may includeidentifying a potential weakness in the operating characteristics of thepulsed-output laser based on the analyzing the first single-pulse lasingevent and using the potential weakness in the selecting the second inputpulse stream.

These quick settling methods operate to reach settling of apreviously-specified pulsed output operation within a small number ofrepetition periods. The method may create pulsed outputs with degradedsingle pulses, with multiple pulses, or with multiple peaks during theprocesses of creating a new input pulse stream intended to create asingle output pulse within specification under the new operatingparameters. In one embodiment, the method includes creating degradedpulses (and performing other steps of the method) for a number ofrepetitions (e.g., repetition periods) before an input pulse stream issent to the Q-switch(es) that is intended for operating the laser with anon-degraded single pulse that is intended to meet specification if itis output from the laser. In other words, there may be any number ofrepetitions of degraded pulses for producing information to analyzeabout the present operations of the laser. In some embodiments, thesedegraded output pulses, and any other intermediate output pulses (e.g.,from the start of the method through creating the input pulses intendedto create a specification-meeting output pulse) may be shuttered and notproduce an optical output from the system.

Therefore, the innovative methods described herein for settling on adesired input pulse stream (and other laser input parameters) forcreating a pulsed laser output within specification may be takenstep-wise via either of these two types of processes (degraded pulsegenerating or corrective pulse generating), or any combination of thetwo processes, for seeking the next input pulse stream that will be usedto create the next output intended to be within specification.

Both corrective and degrading types of processes described herein canbegin with the same condition: a normal input pulse stream (e.g., oneintended to create an output pulse within specification, one that hasbeen consistently used to create output pulses within specificationrecently). The intentionally-corrective input-refining process includessteps that provide a next input pulse stream is modified by anincremental change to one or more portions of the pulse stream or alaser operating parameter (e.g., pump power) is determined based on thedifferences between the pulsed laser output and the pulse specification,and that is targeted at reducing this difference/error in the nextoutput repetition. The intentionally-degrading input-refining processincludes steps that provide a next input pulse stream that is determinedbased on the differences between the output and specification, andtargeted at reducing the corrective repetitions made by the laser viacreating one or more degraded interim outputs (e.g., pulsed lasingevents) that allow processes herein to analyze the laser beforedetermining a next set of input pulse streams and sending it to thelaser to create a pulsed output within specification. In severalembodiments, these intentionally degrading processes actually createmore errors in the output pulses (e.g., double pulses, further outsidespecification) during the subsequent pulsed output repetition. Asdescribed further herein, this change may be intentionally made in orderto produce an output that is designed for analyzing the laser viaproducing degraded output of the laser.

An explicit example of one embodiment for the fast-settle processincludes the following steps during initial manufacturingcalibration. 1. Create an output pulse meeting specification throughadjustment of the laser control parameters. 2. Take ΔT from previouspulse and increase ΔT by an amount of approximately 5-10× the desiredoutput pulse width in order to create an output pulse doublet. Forexample, for an input pulse with a ΔT of 70 ns, an intentional output ofa pulse doublet may be created by increasing ΔT by 50-100 ns. 3. Measurethe amplitudes and pulse spacing of the resulting output pulse doublet.4. Measure the response in time and amplitude of each pulse in thedoublet to small changes in HV1 via modifying the HV1 slightly or over abroad range for a number of repetitions of lasing events by the laserwith different HV1 values. 5. Record the characteristics of the severalprototype waveforms of the input pulse streams and the doublet responsesto a system memory for use in controlling the laser.

In one embodiment, once the laser is characterized with prototypewaveforms in memory and is operating, the following steps describe afast-settle method to create an optimal output pulse shape in thepresence of unknown environmental perturbations. 1. Increase ΔT from theprevious pulse's ΔT value by one of the amounts previously used duringpulse doublet characterization described above. 2. Measure theamplitudes and pulse spacing of the resulting output pulse doublet. 3.Compare the pulse doublet measurements to the data stored in controllermemory. 4. Determine a correcting action (e.g., to HV1, to ΔT) for thenext attempted single stretched pulse lasing event based on the storedresponse rate. 5. Optionally generate an additional pulse doublet lasingevent and repeat the process (e.g., part of the process, through thedetermining a correcting action step) in order to verify the previousdetermination of the corrective action. 6. Remove the extra ΔT added instep 1 and begin repetitive laser operation with corrective actiontoward an optimized shape of a single output pulse.

Another embodiment here describes a slow-setting technique to create ashape of a single output laser pulse meeting specification. 1. IncreaseΔT from the previous pulse's ΔT value by an amount of approximately 10×the pulse width (in this case 50-100 ns). 2. Create a pulse doubletoutput from the laser and compare the amplitudes of the resulting outputpulse doublet. 3. If the first pulse is lower in amplitude than thesecond pulse, increase HV1 slightly and go back to Step 2. If the firstpulse is higher in amplitude than the second pulse, decrease HV1slightly and go back to Step 2. 4. If the pulses are approximately equalin amplitude decrease ΔT slightly and repeat from Step 2 until theoptimal waveform is obtained.

In one embodiment, a degraded settling process includes only a singleintentionally-degraded pulse input and output that is processed asdescribed further herein, and thereafter the process seeks a desiredinput pulse stream via an incrementally corrective process withoutintentionally degrading the waveform first. For example, the differencesbetween a degraded output pulse and the expected pulse may be used tocreate a weighted estimation of an input pulse stream that iscorrective. As shown above, the responses to changes in the input streammay be relatively consistent, and thus a weighted estimation at acorrected input stream may be calculated based on the differencesmeasured on the degraded output. For example, a desired output changemay be calculated directly from analysis of the degraded input/outputpair. In one embodiment, this weighted estimation may be calculatedquickly enough to influence the next input pulse stream delivered to theresonator at the repetition rate. In this embodiment, there may be onlyone degraded input pulse stream and its associated output pulse streamduring a fast-settle process before another step-wise correctiveincrement is made in the input pulse stream. In other embodiments,multiple degraded inputs and output repetitions are used to calculate aweighted estimation of a next corrective input pulse stream to send tothe resonator. To be clear, whenever the next corrective input pulsestream is calculated from the degraded input steps, that next correctiveinput pulse stream will embody a large shift from the degraded inputpulse stream, with the intention of receiving a pulse output from theresonator that is much improved. From this first corrective input/outputcycle, a step-wise process may be then used to settle the input pulsestream to create the desired output. In some embodiments, anotherdegraded pulse stream process may be later initiated to measure quicklydifferences in the resonator performance (e.g., based on storedcharacterizations of the resonator's performance) and to discerncorrective changes that need to be made.

As described above, settling processes disclosed herein allow lasersystems to settle on a desired input pulse stream assuredly and within aminimum number of corrective repetitions (e.g., repetition time periodsbetween when the process starts and settling on an input pulse streamthat creates consistent repetitions of pulsed outputs withinspecification. As used herein, the term “corrective” when used indescribing changes made to the input pulse stream means that the nextoutput pulse is intended to incrementally move the output pulse towardspecification. For example, when a direction is identified in which tomodify an input parameter (e.g., increasing HV1, decreasing delay) thena corrective change in the input pulse stream is made and used to createa new pulse output before analyzing the output and thereafter, eithertaking another intermediate step along that same direction or anotherstep in another direction. As used herein, the term degrading means thatan even after such a direction is identified (e.g., after such adirection could be identified). In several embodiments of fast settlingprocesses described herein, the analysis steps include determining avalue for an input parameter that does not create input pulse streamthat creates a degraded pulse output but rather than a corrected outputpulse or lasing event.

As described herein, the term repetition rate applies to an expected ordesigned repetition rate of pumping and pulsing the laser, such asrequired by specification or as achieved in actual practice. Often, therepetition rate demands many repetitions per second (e.g., 10-20 Hzrepetition) and the laser may be set up to cycle each 100 ms regardlessof the desirability of outputting each pulse. For example, describedherein are methods that intentionally create degraded pulses that couldbe desired to be shuttered, kept internal to the laser, or otherwise notoutput along the normal output route. In some embodiments, such asduring testing phases, there need not be an output from the laser foreach lasing event within the laser. For example, input pulse streams maybe sent to the laser and create lasing operation that results in adegraded output pulse, that is blocked (e.g., shuttered) from outputtingfrom the laser (e.g., outputting through a usual output). Instead, asdescribe herein, when the laser is described as having a lasing event(e.g., a pulsed lasing event), the laser light may develop or remainwithin the laser resonant path (e.g., shuttering or shunting the lasingevent from outputting from the laser), the laser light may be shunted ordirected to another part of the laser (e.g., a detector, an absorber),and/or the laser light may be output from the laser. Therefore, asdescribed herein, the terms repetition or lasing event need not resultin lased light emerging from the laser. Instead, as shown in FIG. 16,the intracavity fluence may be sampled or sensed and substituted forcontrol actions used and described herein.

In one embodiment, a laser may be developed and used with a storedmemory with multiple operating parameters based on certain operationalconditions and processes described herein, such as various temperaturesof portions of the laser and related starting conditions or processes.In these stored processes, the laser may have access to multiplesettling operations, including resetting pulsed laser output to newstarting conditions, such as to restore proper pulsing operation, andseveral processes for maintaining pulsed laser output operation whileoperational conditions are changing, with each method being selectableby the laser system for use during operations. Thus, as describedherein, any of the sensed or analyzed information of an output laserpulse may be used to determine the input to the laser (e.g., inputQ-switch loss condition and/or pump energy) for next or a subsequentpulse generation.

For example, in one particular class of embodiments, methods aredescribed herein for setting pulses in a controlled environment for arange of operational conditions and storing the associated Q-switch lossconditions (e.g., values for HV1, Delta T, and HV2) for settling pulsesduring each of these operational conditions. During operation this lasersystem may use the stored data to select starting values for pump energyand Q-switch loss conditions. In one such embodiment of a method, thelaser system uses a particular Q-switch loss condition for generatingpulses and maintains and adjusts the shapes of repeated pulses bymodifying only the gain of the laser via changing the energy deliveredvia pump energy. In some options for this class of embodiments, a methodmay not be able to maintain a repeated pulse using one of the presetQ-switch loss conditions with modifications only to the pump energy andmay thereafter implement a separate method for settling a pulse. Forexample, a method may initiate a reset method, a quick settling method(e.g., with a degraded pulse) or an initial pulse settling method. Eachof these methods may also be available for the laser system to find newloss conditions and pump energies to perform either an automatic resetof the pulse-generating conditions or have manual reset option formanual or semi-manual intervention.

As one example, an embodiment of a method includes adjusting a Q-switchloss condition and a pump energy to settle an pulsed laser output undera certain (set of) operating condition(s) and storing that Q-switch losscondition and pump energy with the operating condition(s) in a memoryaccessible by the laser. The method includes operating a pulsed laser bysending a first input pulse stream to a Q-switch in the laser such thatthe laser creates a first single-pulse lasing event in the laser. Themethod records in a memory device the first input pulse stream such thatis correlated with at least one first operating parameter of the laserand first sensed data about the first single-pulse lasing event of thelaser. Based on receiving indication that the at least one firstoperating parameter has changed, the method operates the laser with asecond input pulse stream to the Q-switch such that the laser creates asecond single-pulse lasing event in the laser. Thereafter, the methodrecords in the memory device the second input pulse stream, the changedat least one first operating parameter, and second sensed data about thesecond single-pulse lasing event of the laser. Thus, the method maycreate a database of information from which processes may access mayforms of information about how the laser system settles in certainoperating conditions and how to begin a settling process under theseconditions.

In one embodiment, the method includes that the changed at least onefirst operating parameter is a changed delta time, different from afirst delta time measured between a first rise in the first input pulsestream and a second rise in the first input pulse stream. As describedherein, the controlled delta time may be used to separate further amerged pulse (e.g., due to combined intracavity fluence of FIG. 15) orto bring together a pulse doublet and each of these conditions could becreated by a change in operating conditions.

In one embodiment the method includes modifying the first operatingparameter to create an additional changed at least one first operatingparameter in order to provide an intermediate point between at least twoother values of the at least one first operating parameter that havealready been recorded. Thus the method may create additional granularityin the data stored in the database for operating the laser underoperating conditions in an operational environment. As the memory may bepopulated while under controlled environmental conditions, the methodmay change these parameters and sense changes in the pulses, possiblystoring both the sensed pulse data and the operating parameter andallowing methods herein to include same into their settling processes.In one embodiment, the method includes receiving an indication of asecond operating parameter has changed to a changed value and thereafterstoring the second sensed data with the changed value of the secondoperating parameter.

FIGS. 4 and 5 illustrate the diagrammatic construction of linear andring resonators, respectively, with output parameters adapted to targetmarking may be adapted using the methods herein to operate as targetdesignators based on the improvements to the output pulses. When usingthe methods described herein, each of these lasers may include theintracavity fluence shown in FIG. 15, while also demonstrating thepulsed laser output that is output coupled in the stretched formatshown. Because the bulk of the disclosure herein pertains to methods forsettling Q-switched laser resonators, a general framework for discussionis presented below. FIGS. 4 and 5 show two exemplary resonant cavitiesgenerally depicting a resonant cavity including a Q-switch in resonantcavities used in experiments described herein that may be furthercomplicated by folding the cavity, twisting the cavity, creating aresonant path on more than one plane, or otherwise configuring theresonant cavity to be particularly compact.

The methods included herein can be used in resonators such as thosedescribed in U.S. patent application Ser. No. 15/225,805, which isincluded herein by reference for all purposes. For example, the methodsdescribed herein may be adapted for use with compact resonators thatutilize any combination of image rotation and polarization outcoupling,such as in a specially-adapted ring resonator. Several specializedresonators that track polarization and/or image rotation may use thesemethods to provide additional pulse width stability and/or fast settlingon input parameters to generate output pulses meeting specification.

These methods may be also used with less-advanced resonators that do notuse polarization rotation, image rotation, and/or polarization outputcoupling. These resonators may also benefit from the methods herein forexpanding pulses to meet standard and/or achieving repeatable stableoutput pulses in a variety of settings.

As noted further herein, the description of two Q-switches may bealternatively implemented in electronics. The alternative embodimentswill be described herein with reference to multiple Q-switchesdesignating two separate portions of the described input pulse streams,such as shown in FIG. 6. However, each example may be understood asequally applicable to all electronics instantiations shown and describedherein for a compact resonator with only one Q-switch, including singleQ-switches with multiple signal inputs for receiving different portionsof the described input pulse train. Each Q-switch may be comprised ofone or more crystals or other optical elements.

FIGS. 6 and 13 show and describe an embodiment using only a singleQ-Switch (Pockels Cell) with two signals/conductors each separatelycarrying a single pulse timed against each other (e.g., separated byDelta T) to combine into a complex driving waveform of the Q-switch losscondition at the crystal.

As shown and described with respect to FIG. 7, the Reflectivity R of theQ-Switch is combined and based on the high speeds required, thereflections of the signals may be managed at the crystal, includingimpedance matching or termination calculations for the signals. Suchelectronics are shown in FIGS. 8 and 13, while real-world signalsdelivered to the Q-switch based on the reflectivity and impedancematching is shown in FIG. 14. In some embodiments, the separate signalsmay be carried as one or more differentially driven pair(s) of wires. Insome embodiments, the signals are separately driven with respect to acommon ground carried with the signals. In some embodiments, the signalsare driven with a ground attached to the crystal.

As shown diagrammatically in FIGS. 6, 13 and 14, this separate controlof either side of the crystal allows for complex waveforms to begenerated at the crystal. For example, the rising voltages in FIG. 6 forthe Va pulse may be sent earlier than the rising voltage of the Vbpulse, such as by a time difference of ΔT. These signals combine at theQ-Switch to create a complex signal Va-Vb. In order to create thecomplex signal (Va-Vb) at the crystal, the separated voltage pulses mayoverlap for a period of time. This overlap causes a summation within thecrystal of the voltage pulses peaks for a period of time to reach thepeak of HV2, and these peaks may be further controlled as describedherein to control the pulse output.

Alternatively, FIG. 13 shows a combination of capacitors driven withseparate high voltage drivers connected to the single Q-switch viacoaxial cable. Similarly, FIG. 8 shows the physical boxes for similardriver circuitry for driving either side of a Q-switch. As shown, eachof these electronics components are significant and their size and thesize of the driven signals must be considered when reviewing ideal ramprates and input signal characteristics. FIG. 11 shows additionaloverlaps and creations of the Q-switched drive signals in real-world andcombinations at the Q-switch, such as described in FIG. 6, along withresulting pulsed laser output waveforms.

FIG. 9 shows an exemplary embodiment for a feedback system that allowscontrol of pulse in between pulse repetitions and uses a pump energycontroller as the only controlled quantity for subsequent pulses, andotherwise using the same Q-switch loss condition of HV1, HV2 and DeltaT. As described herein, the term “subsequent” with respect to asubsequent input pulse stream or a subsequent laser pulse in the cavityreferences only a later pulse in the respective pulse stream and notnecessary the directly next pulse after the next pulse repetitionperiod. Instead, where discussed as the directly next pulse after thenext pulse repetition period. As described further herein, each of thelaser pulses in the laser cavity may directed out of (e.g., output from)the laser cavity or directed to a detector or may be otherwise sensed.

Described herein are embodiments of methods for developing andmaintaining repetitive laser pulses that are developed and maintained inpulsed repetition in a first environment (e.g., in a lab or factory, inan environment that has heat/temperature control) during a first phaseof the method by using a first set of control variables sufficient todevelop the repetitive pulses while maintaining a first input power or aset of powers within a range around a first input power (e.g., abaseline input power and an indication about a range). The methodsthereafter include various embodiments of controlling the output shapeof the laser via controlling an aspect of the input power while thelaser is operated in a second environment that is different from thefirst environment (e.g., in operational deployment environment, in anenvironment with an uncontrolled temperature). The methods herein limita set of operating parameters (e.g., the input pulse stream) foroperating in the second environment, operating from a fixed set of inputpulse stream parameters for modes of operation in the second environmentbased on results from a prior operating of the laser in the firstenvironment.

Methods herein describe fixing a loss and modifying a gain by modifyingan input energy to the gain element for use in a subsequent pulsegenerated in the laser cavity. Particularly described herein are methodsthat use a fixed set of input pulse stream parameters that determine thetiming and magnitude of the loss provided in the laser gain cavity bythe input pulse stream being delivered to Q-switch or other controllerof loss in the cavity. Thereafter, the gain for producing a subsequentlaser pulse is controlled via input energy parameters to the gainmedium, such as energy parameters for a pump diode array. The inputenergy parameters can include all things affecting energy delivered tothe gain medium, whereby the gain of the gain medium inside the lasercavity will be an exponential relation as the integral of input pumpdiode current over the pump time that the pump is operational. Thevarious input energy parameters may be stored and fluctuated by adigital signal processor that has received an indication of the laserpulse generated in the laser cavity.

FIG. 9 illustrates an embodiment of a laser operating with a feedbackmethod as described herein. The laser produces a laser pulse within thecavity that is sampled as described herein (e.g., output from thecavity, split to detector) and then detected by a detector. The sampleof the laser pulse is detected by a detector that can have a severetemperature fluctuation. A detector may fluctuate on a baseline andabsolute measurements, however, as described herein, the shape of thepulse may be used to determine the adjustments needed to be made to thegain and energy directed to the gain medium. In addition, othercomponents associated with the energy in and energy out measurements mayfluctuate in their operation with temperature.

The pulse shape of the laser pulse generated in cavities describedherein is designed to be relatively independent of temperature due toprior design innovations. However, also in these cavities, when the losshas been encoded as described herein with an input pulse stream, thepulse shape is strongly correlated with input energy and the gainexhibited by the gain medium. The efficiencies of these energy systems,including the transfer of energy between them, are each stronglydependent on operating temperatures of components in the laser system,and thus the energy measurements may be largely skewed by varioustemperatures of the components. The methods described herein use abaseline energy in the beginning of developing a pulse and correctionsare made from that baseline. In some embodiments, multiple baselineenergies are provided for selection based on large scale or macroscopicoperating environmental factors. Therefore, as described further herein,in one preferred embodiment, a baseline energy is used to create a firstlaser pulse that is detected or sensed, and the pulse's detected shapeis used to determine a gain modification by determining a shape changeto be sought for a subsequent laser pulse, and thereby correlating thatshape change with a gain modification to be made for that subsequentpulse. This provides one of the most compact feedback methods fortemperature stability of pulse development and maintenance of all thedescribed methods herein.

In another embodiment, the methods described herein may be used toproduce a stabilized and predetermined pulse energy because it is aparticular pulse energy that we are selecting by using the baselines.These baselines are coupled to a loss encoding for the cavity such thata selected energy input, when combined with a specified loss condition.By selecting certain methods herein that fix much of the control of thelaser by encoding the loss to the characteristics of the specificcomponents used in the cavity, these embodiments of the methods providea process by which a laser pulse with a determined output energy (orenergies) in a first environment (e.g., laboratory) may be matched to aloss combination with a baseline energy data (single baseline or set ofbaselines) in order to operate exactly on that same predetermined outputenergy (or energies) in a subsequent operating environment (e.g., field,inside other equipment). Thereafter, the energies of the output may beadjusted by these methods based on analyses of the shape of the pulse,as described by the methods herein. Thus, the methods can create anenergy stabilization of the output laser pulse by direct feedback usingonly the pulse shape in order to create a feedback method that allowspulse development and maintenance that is independent of the presentoperating temperature, humidity, and other environmental effects on thesensor (e.g., sensitivity, gain, bias) and other energies produced ortransmitted by the laser.

As shown in FIG. 9, a pulsed laser output is sampled, shown as apartially transmissive/reflective element that samples a portion of thepulse to a detector. In one embodiment, the partiallytransmissive/reflective element is outside the cavity. In anotherembodiment, the partially transmissive/reflective element is inside thecavity and does not interfere significantly with the operation of thecavity. For example, the partially transmissive/reflective element maybe placed inside the cavity as a mirror that is only very slightlytransmissive and the detector may be placed behind the mirror. Whilethis embodiment would put the detector outside optical path of thecavity, a sample of the circulating cavity intensity would be detectedoutside the cavity via a partially transmissive element inside thecavity.

Alternatively, a turning mirror may be used in the cavity with anincomplete reflection and a partial transmission may be used to samplean intensity of the laser pulse by placing a detector behind the mirror.The partially transmitting mirror may be placed downstream from thecavity or within the cavity itself. The partial transmission may becaused by diffuse scattering or ways of creating partial reflection. Inone embodiment, the pulse may be sampled by using a partial reflectionfrom a window that primarily transmits the pulse out of the cavity, butalso reflects a small amount into a detector. In one embodiment, thepartially reflecting window may be placed downstream from the cavity orwithin the cavity itself. The partial reflecting may be diffusereflection. The diffuse reflection may be from an undersized aperture.

Each of the elements described herein includes a real-world delay, andthus discussions of relative timing of signals, such as relative timingof input pulse streams and output pulse streams, the term relativeincludes as measured relative to events of the Q-switch loss condition,such as voltage ramps described herein. For example, the detector andother components relating to powering of the laser are subject to bias,drift, gain fluctuations, sensitivity changes and other changes based onthe operating environment is subject to thermal fluctuations, soappropriate scaling may be performed during or before shape analysis bya pulse shape analyzer. The pulse shape analyzer may operate asdescribed herein.

The above functional diagram may be instantiated in any form of digitalsignal processing architecture, as described by the function arrowsbetween the detector, the laser, and the electronics, the informationmay be passed as known in the art between functional units, which theythemselves may be similarly instantiated. For example, a programmablemicroprocessor (e.g., FPGA, DSP) may be used as pulse shape analyzer,and the microprocessor may be integrated with an analog controllingportion on a single package. Other connections may be made to meettiming constraints to process a pulse and provide an input stream andpulse energy in time for the next pulse that is intended to be changedby the energy modification (or other input modification, in otherembodiments).

In order to meet repetition rates, these changes must be determined, andanalog circuitry must be activated within repetition periods that arevery short, therefore the timing of the determinations must be made withrespect to the window in which the determinations may be made and inputparameters may be changed. For example, an energy delivered to a gainmedium may be delivered from a pump diode, and the pump diode must bedriven by a maximum current over a period of time to deliver the desiredpower. In this example, power may begin being be delivered before afinal determination of the energy to be delivered to the gain medium iscompleted. Thereafter, the method may finish determination of totalenergy for subsequent pulse and complete delivering power based on totalenergy determined.

Other analog components may have similar set up times that need to bemet by the described methods and digital and analog processing, forexample, in order to meet a particular repetition period for a pulsedoutput of the laser.

FIG. 10 shows shape identifiers to be used in determinations of whethera laser has a defect in the amount of gain, by how much and how toadjust the gain delivered by a laser gain medium a subsequent laserpulse from a subsequent input pulse stream (e.g., using fixed parameterscontrolling loss of the laser cavity) where those determinations aremade based on the shape of the laser pulse created by the cavity (e.g.,inside the cavity, outside the cavity) and gain changes are maderelative to a fixed loss framework of the laser cavity including a fixedHV1, fixed HV2, and delta T portion. The data in this figure issimilarly described herein with respect to shapes of pulses with respectto the various amounts of loss relative to a fixed or constant gain.Thus, these figures relating gain and loss to output pulse shape providesupport for and describe details of the methods herein for controllingthe pulsed output (e.g., in an operating environment) based on thegain/loss ratio provided by the cavity.

Shown in FIG. 10 are shapes of output pulses showing a late skew (andanomalous peak) for pulses with 1% less gain than nominal/predeterminedfor operation and an early skew (and anomalous peak) for pulses with 1%extra gain. By using these shape identifiers in these methods, asdescribed herein, a gain modification can be determined for correctingchanges in the gain that have occurred in a second environment.

As described herein, there may be many processes and shape identifiersaccessible to the laser for settling the pulsed outputs and in someinstantiations, these feedback controllers may include limited control.These methods and data may be stored in, near or accessible to the lasermay be data and memories including methods of creating laser with lookup tables and databases of operating in different conditions, methods ofoperating lasers with these data, methods including receiving laser,operating laser, producing reset, and all portions of these settlingmethods.

The stored memory can include many different shape determinations to aidin analyzing the shape of the output of the pulsed laser output and forcontrolling the subsequent pulses under particular methods fordeveloping and maintaining the pulses described herein. Described hereinare many different types of methods for determining modifications foradjusting the laser operation in response to different problems orissues encountered in producing the pulsed laser output. As describedabove, there are many complex interactions within the laser that areinvolved with producing the desired stretched pulsed laser output. Insome embodiments, the methods for producing and maintaining the pulsedlaser output are specifically limited to certain modifications toprovide alternative pulse maintenance and control, such as limiting theamount of control on modifying the instructions to the laser forproducing the next pulse or some subsequent pulse, such as via limitinga change to the pulsing instructions to a particular change in a portionof a Q-switch loss condition or in the pump energy for the a subsequentrepetition or the next repetition of the pulsed laser output.

In one embodiment, the stored method may be created while in oneenvironment and then operated while in a second environment, usingstored Q-switch loss conditions and changing only the pump energy. In afirst environment, the method operates a laser cavity including apumping source of a gain medium within the laser cavity, the operatingthe laser cavity including the using of an input pulse stream thatcontrols a loss condition of the laser cavity to produce a laser pulsewithin the laser cavity that meets one or more specified outputparameters for the laser pulse. The input pulse stream includes an HV1input pulse with an HV1 voltage, an HV2 input pulse with an HV2 voltage.The input pulse stream comprises a combined signal of the HV1 inputpulse and the HV2 input pulse with a delta time separation between afirst rise in the combined signal to an HV1 voltage and a second rise toan HV2 voltage.

In this embodiment, the method further includes first recording fixedinput pulse stream parameters including the HV1 voltage, the HV2voltage, and the delta time separation in a digital memory. The methodfurther includes second recording an indication of baseline input energyfrom the pumping source that was used during the operating the lasercavity step for pumping the gain medium related to performing theoperating the laser cavity. The method further includes first preparingthe laser to operate with the fixed input pulse stream parameters as aset of fixed operational parameters in a second environment in thefuture, wherein the second environment is different from the firstenvironment. The method further includes second preparing the laser tooperate in pulsed mode operation to produce a second laser pulsegenerated after the laser has left the first environment and while thelaser is in the second environment. The method includes second preparingthe laser to operate in pulsed mode operation to produce a second laserpulse generated after operating the laser cavity to produce the secondpulse laser pulse while the laser cavity is in the second environment.The second preparing the laser to operate in the second environmentincludes preparing to operate while using a range of input energyparameters that includes the baseline input energy of the pumping sourceand to operate within the range of input energies around the baselineinput energy, selecting the input energy for a subsequent pulse based ona received indication of the second pulse laser output, whereby thereceived indication of the second laser pulse is processed by a digitalprocessor.

In this embodiment, the digital processor is programmed to perform thesteps of (1) determining a shape identifier of the received indicationof the second laser pulse, (2) determining a correction to a subsequentinput pulse stream from the shape identifier of the received indicationof the second laser pulse, (3) wherein, if the shape identifier includesan early skew or early anomalous peak relative to the second rise to theHV2 voltage, determining that the correction is a decrease in inputenergy for the subsequent input pulse stream, and (4) wherein, if theshape identifier includes a late skew or late anomalous peak relative tothe second rise to the HV2 voltage, the correction is an increase ininput energy for the subsequent input pulse stream.

In one embodiment, the shape identifier is determined to include amonotonic rise to the early anomalous peak of a skewed-early pulse, andthe correction is a second increase in the input energy for thesubsequent input pulse stream, the second increase in input energy beinggreater than the first increase in input energy. In one embodiment, theshape identifier is determined to include a rise to the early anomalouspeak relative to the second rise to the HV2 voltage and followedthereafter by a late anomalous peak, and in this embodiment, thecorrection is a second decrease in the input energy for the subsequentinput pulse stream, the second decrease in input energy being greaterthan the first decrease in input energy. In one embodiment, thesubsequent input pulse stream is adapted to be used to generate a thirdlaser pulse after the second laser pulse, and potentially manysubsequent pulses if the method has found a working Q-switch losscondition and pump energy combination. For example, the second preparingto operate the laser may include preparing the laser to operate with arepetition period between at least two pulses being generated, andwherein the third laser pulse is a next-generated laser pulse in thesecond environment with one repetition period between the second laserpulse and the third laser pulse.

In one embodiment, a method may operate a laser with pre-stored dataabout operational parameters in an operational environment without themethod characterizing that laser or placing that data with the laser.The method includes, while in an operational environment, operating alaser with a set of fixed input pulse stream parameters as fixedoperational parameters and adjusting an input power source including thebaseline input power parameter of the pumping source between subsequentoutput pulses in order to settle those output pulses. The methodoperates within a range of input power parameters based on feedback froma pulsed laser output produced when the laser output is processed by adigital processor to determine a shape identifier of the pulsed laseroutput. The method includes analyzing a shape of the pulsed laser outputincluding an indication of an early anomalous peak or a late anolmolouspeak (early or late skew). The method thereafter selects the inputenergy for a subsequent pulse based on a received indication of thesecond pulse laser output, within a range of input energy parametersaround the baseline input energy.

As shown and described with respect to FIGS. 3 and 10, thesedeterminations for subsequent pulses may include multiple parameters, inaddition to changing the pump energy for a subsequent pulse. Manycomplex requirements for creating the intracavity fluence (E_IC) and theoutcoupled laser pulse (E_OC) shown in FIG. 15 for a stretched pulse asdescribed herein. These multiple parameters that may be changed inresponse to the conditions of a sensed/analyzed pulsed laser output mayinclude multiple options for change that may lead to losing control ofthe settled pulse.

There are several alternatives to controlling the pulsed laser outputsolely with the pump energy. Any of the changes detailed with respect toFIG. 3 may be used to create a similar set of shape identifiers specificto changes in any input parameter or action detailed therein. Theseshape identifiers and actions may be used thereafter to create similarmethods to those described in detail herein with respect to pump energy.In the avoidance of repetition of disclosure, the substitutions may bemade as shown in FIG. 3 with varying levels of efficacy given thevarying degrees with which the actions control the conditions of thepulsed laser output. These data may be created and stored as describedherein by using controlled environments and characterization testing,such as in the lab, to create additional data sets and methods for usinga separate single control variable. Thus, the methods described hereinmay be chosen to operate a method of developing and maintaining a pulsedlaser output with any of the control actions described herein, withvarying levels of complexity, as discussed with respect to theoverlapping requirements for creating the internal cavity conditions forcreating stretched pulses.

FIG. 12 shows ideal models for pulse generation with a calculatedQ-switch Voltage wave form (QSV) showing an idealized slew rate thatovershoots the threshold significantly. This again assumes ideal andcontrollable laser operating conditions, showing the timing of aQ-switch loss condition and a resulting stretched pulse for a given pumpenergy that correctly responds to the loss condition. However, withoutthe active feedback and analysis methods for settling described herein,construction of a pulse simply from these theoretical analyses of theQ-Switched resonator can serve to be frustrating or impossible.

Each of these theoretical considerations may be included with themethods and systems for settling a pulse stream reliably andefficiently. For example, embodiments containing fast-settling methodsmay rely on any combination of the theoretical formulations forcontrolling the pulsed-response from a resonator and/or thecharacterizations of the resonator described further herein in order toincrease reliability of settling on a pulse stream. As described furtherherein, there may be stored operational parameters that may be used(e.g., used to measure an operational difference against a present pulseinput and/or pulsed output) to create simplified pulse-settling methodsfor reliably and quickly settling on a pulse given a starting set ofparameters.

As described above with the step-wise corrective process, the methodsherein may select a new pulse based on differentials based oncomparisons with known deviations in the gain or other operatingparameters in the resonator. Specifically, a differential may bemeasured between the delivered input pulse stream and the measuredoutput pulse and any number of established pairs of input pulse streamand output pulse, such as those that have been calculated. As describedfurther herein, this next established pair for creating a differentialmay be a pair containing a degenerated output pulse stream such as apulse doublet or a degraded single pulse. In another embodiment, thenext established pair used for this comparison may also be an attemptedimprovement of the output pulse via changing the input pulse streamusing one of the methods described herein for the step-wise correctivesettling of an input pulse stream to create an output that is withinspecification.

FIGS. 13 and 14 each show particular real-world examples for creatingthese input pulse streams and the electrical complexities for doing so.

FIG. 15 shows the relationship between internal intracavity fluence(E_IC) is different than exterior output (E_OC), showing theinterrelated nature of the controls on the Q-switched loss condition andthe pump energy that change building of the pulse by the reflectivity ofthe Q-switches, all as described further herein. In some embodiments,the laser pulse may circulate in the cavity many times building beforebeing output through one of the output methods described herein,including setting up the loss conditions to create the desired pulsegiven a predetermined value of the input energy, as measured by somemeasurement, also described further herein.

For example, the input energy may be measured as the energy that isproduced by a pump source, delivered to a pump source, delivered to again, or some other measure of energy transfer. As another example,energy may be measured by a current and voltage (e.g., power) asintegrated over a pumping time. As described further herein, any ofthese parameters may be changed in order to change the energy, and hencethe gain of a subsequent laser pulse of the laser cavity.

FIG. 16 shows details of a time-window including a rising edge of thepulsed laser output. This time-window may include around the rising edgeby being gated on a power level of the output or may be timed withrespect to the HV1 voltage rise or ramp value. Also shown is anexemplary process for time-window measuring an element/portion of thepulsed laser output for further analysis and determination.

As shown, a pulse energy for that time-window or a maximum/average valueof the power may be determined. These values may be compared againstknown or expected thresholds for determination. For example, the threegraphs of different pulses may be compared in any value against anexpected value for an expected pulse within specification. For example,if the height/power/energy of data in a time-window around the rising ismeasured by the time-window shown, the value thereof can be analyzedagainst a threshold to determine which direction the pump energy shouldbe changed. If the gated power exhibits a maximum over a thresholdchosen over 15 or 18 MW (exact threshold to be determined for aparticular embodiment of laser), then the gain may be determined to betoo high for the particular Q-switch loss condition used. If the gatedpower exhibits a maximum under a threshold chosen under 12 or 10 MW(exact threshold to be determined for a particular embodiment of laser),then the gain may be determined to be too low for the particularQ-switch loss condition used. If the gated power exhibits a maximumbetween those two thresholds, then the gain may be determined to be“good” for the particular Q-switch loss condition used. As describedfurther herein, multiple analyses and determinations may be made toconfirm that the pulse is in need of no further refinement in theprocessing instructions for a subsequent pulse.

As shown in FIG. 16, there are different measurements that may be alsoused in determining a gain error state or other operating conditionneeding correction, including measurement of full width half maximum(FWHM) of the pulsed laser output. However, this measurement does notdirectly correlate to an action to be taken for a subsequent pulse. Forexample, the lower graph with a “good gain” condition shows a FHWM of14.3 ns which might be within the expected range, whereas the top pulsedemonstrates a FWHM of 8.7 ns for the “high gain” defect state and themiddle pulse demonstrates a FWHM of 12.2 ns for the “low gain” defectstate. As described further herein, a lower than expected pulse widthfor a single stretched pulse can alert that there is an issue, but doesnot provide enough information to fix the error.

These three graphs and separate pulse outputs may be caused as a resultof changing one operating condition, such as temperature and notchanging the pump energy. For example, the lower pulse may becometransformed into either the top graph's “high gain” defect state or themiddle graph's “low gain” defect state simply by changing certainoperating performance characteristics based on a changing temperaturesuch that a new gain/loss ratio is established throughout the Q-switchloss condition and either the timing becomes incorrect or the thresholdsare not properly triggered to create the intracavity fluence shown inFIG. 16.

In one embodiment, the method may include sending a static Q-switch losscondition and only controlling based on changing pump energy based ondetermining a defect as a low energy type defect or a high energy typedefect. The method includes first instructing a Q-switched laser togenerate a first pulsed laser output by sending a first Q switch losscondition starting at a first time and instructing a first pumpingenergy to a Q-switch of the Q-switched laser. As described furtherherein, the first Q-switch loss condition includes a first Q-switchdrive voltage with a first voltage slope of a first rise to the firstQ-switch drive voltage and a transition delta time between the firstvoltage slope and before a second rise to a second Q-switch drivevoltage, with the second rise having a second voltage slope. The methodthen analyzes the first pulsed laser output of the Q-switched laser todetermine whether the first pulsed laser output has a defect of either alow energy type defect or a high energy type defect. Thereafter, basedon the analyzing the first pulsed laser output of the Q-switched laser,the method then instructs the Q-switched laser to generate a secondpulsed laser output by repeating sending the first Q-switch losscondition at a second time and sending a second pumping energy to theQ-switch of the Q-switched laser. As described further herein, thesecond pumping energy is greater than the first pumping energy if thedefect is a low energy type defect and the second pumping energy is lessthan the second pumping energy if the defect is a high energy typedefect.

As described further herein, there are many options for determining withthis method whether there is a low energy type defect or a high energytype defect. In one embodiment, the method receives an indication of adouble peaked pulse in the first pulsed laser output and a peak power ofthe first pulsed laser output and determining that the first pulsedlaser output has a high energy type defect. In one embodiment, themethod receives an indication of a double peaked pulse is an occurrencein the first pulsed laser output above 50% of maximum output power ofthe first pulsed laser output more than three or more zero crossings ofa first derivative in a low-pass filtered version of the output power ofthe first pulsed laser output. In one embodiment, the method receives anindication that a peak power of a rising edge portion of the firstpulsed laser output is greater than a peak power of a falling edgeportion of the first pulsed laser output, and, based on the indication,the method determines that the defect in the first pulsed laser outputis a high energy defect. In one embodiment, the rising edge portion ofthe first pulsed laser output occurs during a first time-window around arising power threshold that is crossed by the rising edge portion andwherein the falling edge portion of the first pulsed laser output occursduring a second time-window around a falling power threshold that iscrossed by the falling edge portion. As described herein, thesethresholds may be determined based on the laser and expectations ofoperations.

In one embodiment, the method further analyzes an indication receivedthat a peak power of a rising edge portion of the first pulsed laseroutput is less than a peak power of a falling edge portion of the firstpulsed laser output, and, based on the indication, determining that thedefect in the first pulsed laser output is a low energy defect. In thisembodiment, the rising edge portion of the first pulsed laser outputoccurs during a first time-window around a rising power threshold thatis crossed by the rising edge portion and wherein the falling edgeportion of the first pulsed laser output occurs during a secondtime-window around a falling power threshold that is crossed by thefalling edge portion.

In one embodiment, the method further analyzes an indication of adifference in time for a rising edge of the first pulsed laser outputreaching an output power threshold relative to a beginning time of thefirst rise to the first Q-switch drive voltage. The method thereafterdetermines whether that analyzed difference in time is greater or lessthan a threshold time. If the difference in time is greater than thethreshold time, the method determines that the defect in the firstpulsed laser output is a low energy defect. If the difference in time isless than the threshold time, the method determines that the defect inthe first pulsed laser output is a high energy defect. For example, asdescribed further herein, a quicker rise of the rising edge of thepulsed laser output (e.g., as gated in a time-window for analysis) maybe used to determine that there is a high energy defect.

In one embodiment, the method further analyzes a power of the firstpulsed laser output during a first time-window of the first pulsed laseroutput, such as may be sampled as described in FIG. 16. The methodincludes comparing the sampled power of the first pulsed laser output toa threshold power. If the sampled data is less than the threshold power,the method determines that the defect in the first pulsed laser outputis a low energy defect. If the sampled data is greater than thethreshold power, the method determines that the defect in the firstpulsed laser output is a high energy defect.

In some embodiments, the analyzed time-window will cover only a risingedge portion of the pulsed laser output. In some embodiments, only a topportion of the pulsed laser output is analyzed, such as wherein the topportion is an upper 50% of the maximum intensity of the pulsed laseroutput.

This patent description and drawings herein are illustrative and are notto be construed as limiting. It is clear that many modifications andvariations of this embodiment can be made by one skilled in the artwithout departing from the spirit of the novel art of this disclosure.While specific parameters, including device configurations, parametersof components, other reference points can also be used. Thesemodifications and variations do not depart from the broader spirit andscope of the present disclosure, and the examples cited here areillustrative rather than limiting.

What is claimed is:
 1. A method comprising: first instructing aQ-switched laser to generate a first pulsed laser output by: sending afirst Q-switch loss condition to start at a first time; and sending afirst pumping energy to a gain medium of the Q-switched laser, the firstQ-switch loss condition comprising: a first initial Q-switch drivevoltage with an initial voltage slope of an initial rise to the firstinitial Q-switch drive voltage; and a first transition delta timebetween the initial voltage slope and before a subsequent rise to afirst subsequent Q-switch drive voltage, with the subsequent rise havinga second voltage slope; determining that the first pulsed laser outputof the Q-switched laser is a single pulsed output of the Q-switchedlaser; second instructing the Q-switched laser to generate a secondpulsed laser output that is a double pulsed output of the Q-switchedlaser by sending a second Q-switch loss condition to start at a secondtime after the first time, wherein the second Q-switch loss conditionincludes a second transition delta time and a second initial Q-switchdrive voltage; and third instructing the Q-switched laser to generate athird pulsed laser output that is a single pulsed output of theQ-switched laser by sending a third Q-switch loss condition to start ata third time after the second time, wherein the third Q-switch losscondition includes a third transition delta time that is shorter thanthe second transition delta time and further includes a third initialQ-switch drive voltage that is smaller than the second initial Q-switchdrive voltage.